1. Field of the Invention
This invention pertains generally to producing facsimiles of physical objects, and more particularly to production of a facsimile with uniform wall thickness and surface topography which matches that of a production stage component.
In the automotive and other industries, models are commonly used prior to the development of production prototypes. In the development process for a new product, however, there is a need for dimensionally accurate facsimiles of proposed production stage components well in advance of the actual production stage.
2. Description of the Background Art
For several decades the automotive industry, as well as the aircraft and boat building industry, has used laminated composite shapes, skins or components constructed of glass fiber cloth bonded with either a polyester, epoxy or urethane matrix. These composites are widely used in boat hulls, racing cars, tooling aids, mockups, aircraft components, and the like.
As a result of the foregoing applications, advanced fibers and cloths made from carbon, graphite or aramid materials began to appear in the marketplace, where they found further use in highly-stressed, critical aircraft components, usually in the form of pre-pregnated cloths which were then cured under heat and pressure in autoclaves. Other early applications of these advanced fiber materials were partial or complete shells of racing cars, boats and airplanes.
It is well known that pre-production facsimiles for those types of applications can be produced from carbon fiber materials by making a master model, forming a single or multi-layer skin over the surface of the master model, impregnating the skin with epoxy, and curing the skin while heat and pressure is applied to the side of the skin which does not contact the master model. As shown in FIG. 8, however, conventional processing techniques produce facsimiles which are dimensionally accurate with respect to one surface only. Facsimile 10 represents a facsimile produced using conventional techniques. Lower surface 12 represents the front side of a facsimile 10 which was fabricated from a master model identical to master model 16 shown in FIG. 1. Surface 12 is the surface of facsimile 10 which was immediately adjacent to the surface 22 of master model 16 and, as can be seen, complements the surface topography of master model 16. Upper surface 14 represents the back side of facsimile 10 to which pressure was applied. Note that the topography of surface 14 does not conform to the shape of surface 12 and that facsimile 10 does not exhibit uniform wall thickness.
For certain applications, these conventional techniques are suitable. However, in critical applications such as those where it is necessary to develop prototypes which have dimensionally accurate external and internal surfaces, conventional techniques fail.
For example, in developing a prototype of an automobile, it is desirable to simulate the complete outer body assembly as well as a complete inner chassis assembly and to coordinate the fitting of parts. This requires dimensionally accurate facsimiles of the actual sheet metal parts that will be used in the production stage. Because conventional techniques are suitable for making facsimiles of only one surface of a model, considerable time is required to shape and fit the facsimiles of the inner chassis components. Conventional techniques are not capable of producing dimensionally accurate facsimiles of components which duplicate the shape of both surfaces, as well as the wall thickness, of the final component.
The reason that conventional techniques for making facsimiles from these materials fail can be seen by referring again to FIG. 1. In areas of a female radius or "fillet" 18 of a master model 16, when a laminate skin is compressed into fillet 18, instead of producing a facsimile which has a uniform wall thickness as desired to duplicate the production component, the area around fillet 18 will be sometimes double the desired metal thickness or more. Conventional facsimile techniques do not employ means to shape and conform the back side of the laminate skin to the surface topography of the master model before pressure is applied. Due to these resultant non-conformities and irregularities, especially in the fillet areas, these parts do not have uniform wall thickness and lack suitable precision to make dimensionally accurate simulations of automotive assemblies.